By winning protection for their boreal forest, indigenous Canadians help slow global warming.

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Green Gotham

Photograph by Anthony Behar, Sipa Press/AP

With seven billion mouths to feed, human agriculture exerts a tremendous toll on the planet, from water draws to pollution, and from energy use to habitat loss. But there is also a growing set of solutions, from organic agriculture to integrated pest management.

More people around the world are taking a look at urban farming, which offers to make our food as "local" as possible. By growing what we need near where we live, we decrease the "food miles" associated with long-distance transportation. We also get the freshest produce money can buy, and we are encouraged to eat in season.

Another benefit of urban farming is that it can add greenery to cities, reducing harmful runoff, increasing shading, and countering the unpleasant heat island effect. Garden plots can help people reconnect with the Earth, and gain a greater appreciation for where our food comes from (hint: not from plastic packages).

Rooftop and patio gardens create peaceful places for relaxation or contemplation, and they can attract tourists—consider the booming businesses that have sprung up around New York City's lush High Line Park. And urban farming can bring jobs to underserved and depressed urban areas.

Although planners have a long way to go, boosters envision soaring vertical farms that will eventually produce most of what we need within a short walk from home. Still, land in cities is often expensive, especially since gardens tend to contribute to gentrification and rising rents. Urban soils can be loaded with lead, arsenic, and other toxins, requiring remediation or replacement before planting can be done safely.

Cramped conditions can limit yields, and getting enough water and sunlight can be concerns.

Still, if the right combinations of new technology, community support, and economic incentives align, it's possible we may soon be munching on skyscraper scallions and avenue arugula.

An early example is the rooftop garden on the InterContinental New York Barclay Hotel, which includes an apiary. The Midtown bees produce honey used in the hotel's kitchen, and they fly to pollinate plants as far as five miles away.

Planting a Revolution

Across town, planters beautify a rooftop in Hell's Kitchen. Big cities like New York host acres of flat, sunny space, which can be put to use growing food or flowers.

Integrated "green roofs" are gradually catching on. In these, a thin layer of soil or other medium supports a dense mat of plants. Such features can be promoted as amenities to renters or buyers, and they win points toward green building certifications.

But it's also possible to start smaller, by setting out a pot or two, even if just on a balcony.

Reclaiming Our Cities

Photograph by Michael Willis, Alamy

A number of inner-city residents around the world have taken a stand against blight by reclaiming vacant lots, medians, and other marginal land for growing space. In Perth, Australia, an organic community farm sprang up along a busy railway line.

Growing fruits and vegetables can help low-income people supplement their grocery shopping, and it can be a source of fresh, healthful produce. Growers can earn supplemental income by selling excess at community events and farmers markets. As such markets grow, they hire full-time staff, often from the community.

One potential concern is that marginal land can have polluted soil, so it is a good idea to get it tested before planting for consumption. Over time, plants tend to clean soil, but professional environmental engineers may be needed to start the process.

Farming the Future

Photograph by Michael Tercha, Chicago Tribune/MCT/Getty Images

Ken Dunn clears snow from a hoop greenhouse at Chicago's City Farm. The nonprofit project sells fresh produce from a stand in the summer and fall and offers CSA (community-supported agriculture) shares to city residents, who pay to partake in nature's bounty.

City Farm transformed an acre of crumbling cement into an operation that produces 25,000 pounds of heirloom tomatoes, carrots, beets, arugula, and herbs a year. The farm provides economic opportunity and attracts throngs of volunteers and visitors in the Windy City.

Several area restaurants buy ingredients from City Farm, from Vie to Nightwood and North Pond. Bruce Sherman, chef and owner of North Pond, praised the farm's produce, telling the group, "The fact that City Farm grows exceptional produce the right way only makes it better."

Movable Farm

Photograph by Andy Kropa, Redux

Chicago's City Farm, a project of the nonprofit Resource Center, is built on movable plates, so the entire operation can be relocated at the end of a growing season if leases change. The farm has occupied several different sites, including the edge of the former Cabrini-Green housing projects.

Rolling Greens

Photograph by Linda Rosier, NY Daily News/Getty Images

Curt Ellis (pictured) and Ian Cheney won rave reviews for their 2007 documentary King Corn, about the drawbacks to industrial agriculture. They built on that success by filling up the back of a 1986 Dodge Ram with soil and planting tomatoes.

Over the past few years, the two friends have driven their Truck Farm from neighborhood to neighborhood, giving urban kids a chance to get their hands dirty, and see how food looks on the (moving) ground. They produced a film on the project in 2011, Truck Farm, and they've enlisted such singer/songwriters as Jack Johnson and Charlie Sutton to attract the crowds.

It's not likely we'll be sourcing the majority of our food from moving vehicles in the near future, but the Truck Farm project shows how thinking outside the garden box can introduce a new audience to natural foods.

Farming to Survive

Photograph by Pilar Olivares, Reuters

In many poor urban neighborhoods, people have long had to grow some of their own food or tend livestock. Pigs can be kept without a lot of space, and they can eat scraps and garbage. This pen in Pamplona Alta shantytown in Lima, Peru, helps feed a low-income family.

Waste and smells can be a problem, which is why many cities have historically moved to ban animal husbandry within their borders. However, rising awareness of hygiene has helped persuade some officials to loosen some restrictions, especially on chickens.

Farming South Central

Photograph by David Butow, Redux

Between 1994 and 2006, a community of low-income, largely Hispanic people farmed a vacant plot in an industrial section of South Central Los Angeles. Eventually, the owner of the land beneath South Central Farm took steps to evict the growers, touching off a series of protests and legal battles that continue to this day.

Celebrities from Daryl Hannah to Danny Glover came out to support the farmers and raise money to purchase the land, but the owner told the Los Angeles Times that he wouldn't sell to them for any price. The developer told the paper he objected to the farmers' protests and alleged that some garden supporters had used anti-Semitic slurs.

The whole ordeal, complete with local political intrigue, was chronicled in the Academy Award-nominated documentary The Garden.

A few of the former South Central growers have found plots in other areas. The original farm boasted up to 150 different species of plants.

The Office Farm

Photograph by Yuriko Nakao, Reuters

An employee harvests veggies grown inside an office "urban farm" in Tokyo. The Pasona Group, an employment and staffing company, established the growing area to foster a work environment that "coexists with nature."